The present invention relates to a semiconductor device, particularly to a semiconductor device having a storage capacitor and wiring including the copper element, which improves reliability and reduces manufacturing processes.
According to recent developments of information and communication apparatus, a semiconductor device such as a DRAM (Dynamic Random Access Memory) has required higher integration and higher accumulation for semiconductor elements (hereafter referred as an element) therein. Then, as an element has been further fined, various problems have also occurred. One of the problems on a DRAM is reduction of a storage capacitance. Because the capacitance of an element is proportional to its area, if the shape of an element was made smaller simply, the capacitance decreases in proportion to the square of a machining dimension. In case that a storage capacitance of a DRAM decreases, power consumption increases and reliability deteriorates since the refreshing is frequently required for compensating disappearance of electric charges. Therefore, even if an element is fined, it is necessary to keep a storage capacitance at a certain or higher level. Up to a 16-Mbit DRAM, the reduction of the capacitance owing to the fining of an element is compensated by making an oxide film forming a capacitor thin, and then the oxide film thickness is approximately 10 nm at present. However, because the thickness of the capacitor insulation film almost reaches the limit, materials having higher dielectric constant has been developed as a capacitor insulation film for a high integration memory of 64-Mbit or more. Then, tantalum oxide (Ta2O5) is studied for 64 to 256-Mbit, and barium strontium titanate ((Ba, Sr)TiO3: BST) and Pb zirconate titanate (Pb(Zr, Ti)O3:PZT) are studied for a 1-Gbit DRAM.
Furthermore, it is necessary to pay attention to selection of an electrode material in the development of the materials configuring the capacitor insulation film. The reason is that when forming a BST or PZT film on a conventionally-used Si electrode, the electrode film is oxidized, and a dielectric film other than the BST or PZT film is formed since a BST and PZT film require high temperature and oxidation atmosphere for forming them. The insulation film formed by oxidation of an electrode film causes a problem that a designed capacitance cannot be secured. Therefore, noble metals such as platinum (Pt), ruthenium (Ru), iridium (Ir), and palladium (Pd), or ruthenium oxide superior in oxidation resistance and heat resistance are studied as materials capable of withstanding various atmospheres for forming a BST and PZT film. Moreover, since PZT is used as a capacitor insulation film not only for a DRAM but also for a FRAM (Ferroelectric Random Access Memory), Pt, Ru, Ir, Pd, RuO2, and IrO2 are studied as electrode materials.
A throughput required for a semiconductor device has been severer year by year and thus, a signal delay is a problem for a device using wiring in which aluminum (Al) is used for a main conductive film. As an alternative wiring conductor to the Al wiring conductor, a wiring conductor which includes copper (Cu) having a lower electric resistance than that of Al as a main conductive film is studied. However, Cu may diffuse in a silicon oxide and thus, may deteriorate performances of a transistor.
Therefore, a barrier metal is necessary to prevent Cu from diffusing, and refractory metals such as TiN, tungsten (W), and tantalum (Ta) are studied as the barrier metal, as described in, for example, NIKKEI MICRODEVICE (pages 74 to 77 on the June issue in 1992).
Wiring using copper (Cu) for a main conductive film (hereafter referred as Cu wiring) as described in the above denotes a wiring film including the copper (Cu) element of which content is higher than contents of the other included elements.
As described above, various materials are studied on each factor configuring elements of a DRAM with improvement of integration and functions thereof. In case of developing a DRAM device, it is important to select out the material which is superior in electrical and mechanical reliabilities and can be manufactured at a low cost compared with the proposed materials. Then, the optimum materials are generally determined for respective factors.
However, if optimum materials are selected for respective factors, different materials are connected with each other at an electrical joint point between them, and thereby a problem occurs that electrical resistance increases. In case of a semiconductor device having a storage capacitor and Cu wiring, if trying to connect a plug including Cu to an extended portion of an upper electrode of the storage capacitor, the problem occurs that contact resistance increases since, for example, Ru serving as the upper electrode of the storage capacitor contacts with, for example, TiN serving as a barrier metal of the Cu wiring at the joint point and thus the different materials contact with each other.
Moreover, resistance against electromigration is deteriorated at the interface between different materials. A design rule of a DRAM has determined a dimension of 0.35 micron for a 64-Mbit DRAM. However, in case that an operation speed and integration of a device are further improved in future, it is estimated that the design rule determines a dimension of 0.25 micron for a 256-Mbit DRAM, and 0.16 micron as further fined for a 1-Gbit DRAM. Naturally, the fining at the above joint point will be further advanced and thus, it is worried that the occurrence of a void due to electromigration or disconnection becomes obvious.
Furthermore, with an aspect ratio of a plug increases, the problem occurs that a barrier metal film is not completely formed on the bottom of a contact hole. The aspect ratio of the plug is further increased as a result of making a storage capacitor structure a three-dimensionally configuration for maintaining a capacitance. As a result, it is difficult to form a barrier-metal film up to the bottom of the contact hole.
Moreover, in recent years, developments of not only a single DRAM but also a semiconductor device configured by incorporating a memory into a logic circuit, which is referred as a DRAM-consolidated logic, is advanced, and process consistency between a logic manufacturing process for mainly manufacturing a transistor and a wiring conductor connecting the transistor, and a DRAM manufacturing process for manufacturing a storage capacitor in addition to the transistor and the wiring conductor. Conventionally, a electrode film forming process of a storage capacitor, and a barrier metal film forming process for Cu wiring are different from each other since different materials are used in those processes, and as a result, it leads to high manufacturing costs.
As described above, introduction of new materials is studied for a storage capacitance and wiring of a semiconductor device such as a DRAM together with the improvement of integration and functions of an element. However, it is worried to increase contact resistance of a joint point between new different materials, to reduce electromigration resistance, to increase a manufacturing cost, and to deteriorate reliability due to introduction of a new manufacturing system or modification of a manufacturing process. Moreover, in case of a DRAM-consolidated logic having a memory circuit and a logic circuit, the consistency between a DRAM manufacturing process and a logic manufacturing process is required.
It is a first object of the present invention to provide a semiconductor device having high reliability. It is a second object of the present invention to provide a semiconductor device lowered in manufacturing costs. It is a third object of the present invention to provide a semiconductor device realizing low contact resistance at a joint point between a material of a storage capacitor electrode and a material of a Cu wiring barrier metal by adopting optimum electrode material and optimum barrier metal material. It is a fourth object to provide a semiconductor device not easily causing a void or disconnection due to electromigration. It is a fifth object of the present invention to provide a semiconductor device capable of forming a Cu wiring film even if a thickness of a barrier metal film is not uniform when forming the Cu wiring film. It is a sixth object of the present invention to provide a semiconductor device making it possible to form a storage capacitor electrode film and a Cu wiring barrier metal film in the same process.
The present inventor et al. performed computer simulation about ruthenium (Ru), platinum (Pt), and iridium (Ir) studied as electrode materials of a storage capacitor in accordance with the molecular dynamics method, evaluated the adhesion with copper, and studied a possibility as a barrier metal for copper wiring. As a result of analysis, it is clarified that peel strengths of ruthenium, platinum, or iridium films are improved as compared to a case of using a conventional titanium nitride (TiN) film, tungsten (W) film, or tantalum (Ta) film as a barrier metal for copper (Cu) wiring because lengths of the unit-crystal-lattice of ruthenium, platinum, and iridium are comparatively close to that of copper. That is, they clarify that each of ruthenium, platinum, and iridium can be used as a barrier metal for copper wiring.
Moreover, according to the computer simulation analysis performed by the present inventor et al., it is clarified that a peel strength of a film against a silicon oxide film is further improved by adding a transition metal such as palladium (Pd) or titanium (Ti) to Ru, Pt, or Ir. Furthermore, they clarify that a peel strength of a film against a silicon oxide film is improved by using conductive oxide such as ruthenium oxide or iridium oxide.
Moreover, they find that it is possible to provide a high reliability semiconductor device which has a low contact resistance at a joint point between the above upper electrode and the wiring barrier metal, and is superior in migration resistance without deteriorating any functions requested for each film by using the same material for the upper electrode and the barrier metal and by using any one of Ru, Pt, and Ir for the materials in a semiconductor device having a storage capacitor and wiring using copper or a copper alloy for a main conductive film.
Moreover, they find that it is possible to provide a high reliability semiconductor device simplifying a manufacturing process without deteriorating functions requested for each film by using the same material for at least one electrode of a storage capacitor and for a copper wiring barrier metal and by using any one of Ru, Pt, and Ir for the materials in a semiconductor device having the storage capacitor and wiring using copper or a copper alloy for a main conductive film.
Furthermore, they find that it is possible to provide a higher reliability semiconductor device by using Ru, Pt, Ir, ruthenium oxide, or iridium oxide to which at least one of the elements Pd, Ti, Ni, and Co is added for a storage capacitor electrode and a Cu wiring barrier metal in a semiconductor device having a storage capacitor and wiring using copper or a copper alloy for a main conductive film.
A conventional semiconductor device has been developed for each factor such as a storage capacitor or a wiring conductor, and an optimum material has been selected for each factor. Noble metals such as Pt, Ru, Ir and Pd or conductive oxides such as ruthenium oxide and iridium oxide are listed as prospective materials of a storage capacitor electrode film. Moreover, TiN, tungsten (W), and tantalum (Ta) are studied as Cu wiring barrier metals. However, a storage capacitor upper electrode and a wiring barrier metal have electrical connecting portion where contact between different materials is forcibly made.
In case of connection between different materials, a resistance value increases at the connection interface. The trend in semiconductor device developments is oriented in the direction of low power consumption and thus high contact resistance becomes obstruction on the manufacturing of a semiconductor device. Moreover, a memory cell is further fined together with improvements of integration degree, a plug diameter is decreased, and a joint point area between a plug and an upper electrode extended portion is decreased. At this portion serving as a different-material contact interface, it is worried that a void or disconnection occurs due to electromigration.
From the viewpoint that unification of materials is necessary to improve electrical and mechanical reliabilities, the present inventor et al. find that a semiconductor which can be manufactured without deteriorating functions of each film is obtained by selecting suitable materials from many combinations.
The present inventor et al. performed computer simulation about noble metal elements such as ruthenium, platinum and iridium studied as storage capacitor electrode materials in accordance with the molecular dynamics method so as to evaluate the adhesion with copper, and study a possibility as a barrier metal for copper wiring. As a result of analysis, they clarify that, because unit-crystal-lattice lengths of ruthenium, platinum, and iridium are comparatively close to that of copper, so that peel strengths of ruthenium, platinum, and iridium films are improved compared to those of conventional titanium nitride, tungsten, and tantalum films.
FIG. 2 shows a result of an analysis of evaluation regarding the adhesion with a copper thin film of films made of materials studied as barrier metals. The horizontal axis in FIG. 2 shows a difference (|apxe2x88x92an|/ap)xc3x97100=A (%) between a minor side an of a unit rectangular lattice on a close-packed-crystal plane configured by the main element of a barrier metal and a minor side ap of a unit rectangular lattice on a close-packed-crystal plane configured by the copper element, and shows a degree of lattice mismatching between a barrier metal material and copper. Moreover, the vertical axis in FIG. 2 shows energy U obtained by subtracting the entire energy of a system under a state in which a barrier metal sufficiently separates from a copper thin film from the entire energy of a system under a state in which the barrier metal has a contact interface on the copper thin film, and shows a value corresponding to a peel strength of the film. In this case, UCu denotes peel energy between copper and copper. From FIG. 2, it is found that adhesions of ruthenium, platinum, and iridium films with a copper film are improved compared to those of conventional titanium nitride, tungsten, and tantalum films. Moreover, as a result of analysis, it is clarified that melting points of ruthenium, platinum, and iridium are higher enough than the melting point of copper and diffusion of copper can be restrained. That is, it is clarified that each of ruthenium, platinum, and iridium completely functions as a copper wiring barrier metal.
Moreover, the present inventor et al. studied a possibility as a barrier metal about palladium which is a noble metal element studied as the same storage capacitor electrode material. However, it is clarified that the melting point of palladium is the lowest among noble metals compared to ruthenium, platinum, and iridium, the adhesion of palladium with copper is deteriorated, and thus palladium is inferior in barrier property against copper.
As a result, the present inventor et al. clarify that each of Ru, Pt, and Ir is a material usable for a storage capacitor electrode material and a copper wiring barrier metal.
A storage capacitor and a wiring conductor are formed on an interlayer insulator film made of a silicon oxide film. Therefore, a peel strength from a silicon oxide film is requested for a storage capacitor and a wiring conductor. FIG. 3 shows results of measuring peel strengths of a ruthenium film and a platinum film with a silicon oxide film according to the scratch test method. The peel load of the vertical axis in FIG. 3 is a value corresponding to a peel strength of a film. A peel strength requested for a film depends on a manufacturing process or an element structure. However, as a result of experiments, it is clarified that film adhesions of a ruthenium film and a platinum film with a silicon oxide film are different from each other and adhesion of a ruthenium film is stronger than adhesion of a platinum film.
Then, the present inventor et al. further performed study and analysis through molecular dynamics simulation in order to obtain a higher reliability film. As a result, they clarify that the adhesion with a silicon oxide film is further improved by adding at least one of the elements palladium (Pd), cobalt (Co), nickel (Ni), and titanium (Ti) to Ru, Pt, or Ir.
FIG. 4 shows dependencies according to an additional-element content to Ru, Pt, and Ir regarding film peel strengths from a silicon oxide film. The horizontal axis in FIG. 4 shows a quantity of palladium (Pd) to be added to a main component element when using palladium (Pd) as an additional element and the vertical axis shows peel energy from the silicon oxide film, which is a value corresponding to a peel strength. From FIG. 4, it is clarified that a peel strength from a silicon oxide film increases from the time when an additional-element content of approximate 10 at. % is added. Moreover, in the case of ruthenium oxide and iridium oxide, adhesions of their films with the silicon-oxide film are increased.
Furthermore, addition of an impurity element to Ru, Pt, or Ir produces another effect. A stress produced in a film formation step may cause peeling of a film or deterioration of an element characteristic. After forming a Ru, Pt, or Ir film, a large stress is produced. The large stress may remain in a film depending on an element structure and the remaining stress may cause a defect. That is, it is preferable that a film to be formed is of a low stress.
The present inventor et al. clarify that it is possible to moderate a film stress by adding a material having a melting point lower than that of a noble metal element such as Ru, Pt, or Ir to a Ru, Pt, or Ir film through molecular dynamics simulation. FIG. 5 is an illustration showing changes of internal stresses S remaining in a Ru film according to additional-element contents when performing computer simulation of forming films including palladium (Pd), cobalt (Co), nickel (Ni), and titanium (Ti) on an SiO2 substrate at 900 K and cooling them up to 300 K. S0 shows an internal stress when including no additional element. From FIG. 5, it is found that an internal stress is decreased when an additional-element content is approximate 0.14 at. % or more.
When an additional-element content exceeds approximate 25 at. %, an atomic arrangement of a main material is disordered. Therefore, it is preferable to set the additional-element content to approximate 25 at. % or less.
As a result, they clarify that a semiconductor device further superior in mechanical reliability is obtained by adding at least one of the elements Pd, Ti, Ni, and Co to Ru, Pt, or Ir by 0.14 to 25 at. % as a storage capacitor electrode film and a Cu wiring barrier metal.
Problems of the present invention can be solved by the following configurations.
(1): A semiconductor device comprising a semiconductor substrate; a storage capacitor formed on the main surface side of the semiconductor substrate and being provided with a first electrode and a second electrode arranged so as to put a capacitor insulation film between them; a wiring conductor formed on the main surface side of the semiconductor substrate and including the copper (Cu) element; and a first film formed on the surface of the wiring conductor, wherein a material configuring the first film and a material configuring the first electrode and/or the second electrode include the same element.
(2): A semiconductor device comprising a silicon substrate; a storage capacitor formed on the main surface side of the silicon substrate and being provided with an upper electrode and a lower electrode arranged so as to put a capacitor insulation film between them; a wiring conductor formed on the main surface side of the silicon substrate and including copper (Cu) as the main element; and a barrier metal provided so as to contact with the surface of the wiring conductor, wherein the main element of a material configuring the barrier metal is the same as the main element of a material configuring the upper electrode and/or the lower electrode.
The main element of a material represents an element having the highest content percentage among all elements included in the material.
(3): A semiconductor device comprising a semiconductor substrate; a storage capacitor formed on the main surface side of the semiconductor substrate and being provided with an upper electrode and a lower electrode arranged so as to put a capacitor insulation film between them; a wiring conductor formed on the main surface side of the semiconductor substrate and including copper (Cu) as the main element; and a barrier metal provided so as to contact with the surface of the wiring conductor, wherein the upper electrode extends over an area in which the lower opposing electrode exists; the main element of a material configuring the barrier metal is the same as the main element of a material configuring the upper electrode; and the barrier metal contacts with the upper electrode in an upper electrode extending area out of the opposing lower electrode existing area.
(4): A semiconductor device comprising a semiconductor substrate; a storage capacitor formed on the main surface side of the semiconductor substrate and being provided with a first electrode and a second electrode arranged so as to put a capacitor insulation film between them; a wiring conductor formed on the main surface side of the semiconductor substrate and including the copper (Cu) element; a barrier metal provided so as to contact with the surface of the wiring conductor; wherein the shortest distance between the semiconductor substrate and the first electrode is shorter than the shortest distance between the semiconductor substrate and the second electrode; the second electrode extends over an area in which the opposing first electrode exists; the main element of a material configuring the barrier metal is the same as the main element of a material configuring the second electrode; and the wiring conductor contacts with the second electrode in an second electrode extending area out of the opposing first electrode existing area.
(5): In the above Item (2), the main element of the materials configuring the barrier metal and the upper electrode and/or the lower electrode is selected from the group consisting of ruthenium, platinum and iridium.
(6) In the above Item, the main element of the materials configuring the barrier metal and the upper electrode and/or the lower electrode is selected from the group consisting of ruthenium, platinum and iridium, and the material configuring the barrier metal and the material configuring the upper electrode include at least one type of element selected from the group of palladium, titanium, nickel, and cobalt, the sum content of the selected elements being not less than 0.14 but not more than 25 at. %.
(7): In the above Item (1), the capacitor insulation film is configured by a metal selected from the group of strontium titanate (SrTiO3), barium strontium titanate ((Ba, Sr)TiO3: BST), lead zirconate titanate (Pb(Zr, Ti)O3: PZT) and bismuth layered compound (SBT).
(8): A method for manufacturing a semiconductor device comprises the following steps of:
forming an element on the main surface side of a silicon substrate;
forming an interlayer insulator film on the main surface side of the silicon substrate after the element forming step;
forming a first hole for forming a storage capacitor of a memory section and a second hole for forming a wiring conductor and a plug of a logic section, in the interlayer insulator film;
forming a first film on the side surfaces in the first hole and the second hole;
forming the wiring film and the plug film in the second hole after the first film forming step;
forming a dielectric film in the first hole after the first film forming step; and
forming a second film on the dielectric film and on the wiring conductor after the dielectric film forming step.
(9): In the method for manufacturing a semiconductor device in the above Item (8), the main element of the first film and the second film are selected from the group consisting of ruthenium, platinum, and iridium.
The present inventor et al. examined prior arts about storage capacitor electrodes and wiring materials in accordance with the result of the invention. However, they did not find a storage capacitor electrode and a Cu wiring barrier metal made of the same material selected from Ru, Pt, Ir ruthenium oxide, and iridium oxide. It is disclosed to use Pt, Ru, or Ir as a storage-capacitor electrode material in JP-A-5-90606, 10-321816, 10-270667, 10-12839 and so on. Moreover, it is disclosed to use Pt, Ru, or Ir as a Cu wiring barrier metal in JP-A-10-229084, 8-69980 and so on. However, in the above prior arts, there is no description for suggesting the use of the same material selected from Ru, Pt, Ir ruthenium oxide, or iridium oxide for a storage capacitor electrode and a Cu wiring barrier metal.